This invention relates to processing fluid materials and, more particularly, to a method and apparatus for fluid switching.
Fluids are processed in many different fields for many different applications. It is often necessary or desirable in the processing of fluids to switch from one flow path to another. For example, one may wish to filter fluids, to determine different components or constituents of a sample, to separate fluids, to concentrate fluids, and the like. In each of these applications, the fluids often must be passed through different separating media, filters or dividers. It is also often necessary or desirable in the processing of fluids to utilize centrifugal force or a vacuum as the mechanism for enhancing fluid flow.
For example, in the analysis of samples, particularly biological samples, such as whole blood, serum or urine, one must separate or extract the desired components from the sample for later analysis. Analytical procedures that typically require this step include trace organic and inorganic analyses for environmental control in such areas as monitoring industrial effluents, pesticide run-off in drinking water, impurity and formulation analyses in the food and pharmaceutical industries, and process monitoring in many industrial operations. Typically, these analyses require that the extraction or separation step of the desired sample component be performed manually. Once the extraction is made, the extracted or separated components can be analyzed by any known analytical technique such as thin-layer chromatography, mass spectrometry, gas chromatography, and the like.
One such extraction technique is described by Quame in U.S. Pat. No. 3,567,029. Quame describes the use of a disposable separating column filled with a particular solid phase, capable of extracting certain lipophilic compounds, including the most commonly encountered abused drugs, such as phenobarbital, amphetamine, methadone and the like. In a typical drug extraction, such as from a urine sample, Quame allows the urine sample to pass through the column. The column selectively adsorbs any lipophilic drugs contained in the urine, thereby extracting the lipophilic drugs from the aqueous phase which is passed to a waste receptacle. The receptacle is manually replaced by a recovery cup. Next, the adsorbed drugs are eluted from the column by a solvent which is passed to the recovery cup. This technique works quite well for some urine samples. Unfortunately, however, it is somewhat time consuming because it is manual and because the sample and the solvent phases are slow to pass through the column and filter combination. The application of a vacuum has been used to speed up the flow, but even here required manual switching between different fluids and of the waste receptacle and recovery cup poses a problem.
Another technique for assaying fluids is that described by Shapiro et al. in U.S. Pat. No. 3,953,172. Shapiro uses a swinging bucket centrifuge rotor with the buckets each holding a separating column. The fluid samples to be assayed are mixed with a reagent at the central part of the centrifuge rotor and then allowed to pass, under the influence of centrifugal force, through the separating column. While Shapiro does have the advantage of using centrifugal force to speed up the process, he is still limited somewhat in application, as are the vacuum techniques, in that multiple fluids cannot readily be used to recover the desired sample components from the column. It is even more difficult to concentrate the desired materials for later analyses. No fluid switching is provided, i.e., no means is provided to permit different fluids flowing through a separating column to pass to different collecting vessels. Conceivably, this might be accomplished by various valving arrangements, but such becomes relatively complex and, in any event, apparently has never been accomplished.